The present invention is directed, in general, to network adapters and, more specifically, to an auto-detection system and method for a network transceiver that allows the network transceiver to switch from a first rate mode to a second rate mode automatically.
The reliable operation of computer systems depends in part on the reliable transfer of data both within a particular system and system to system. Many established formats and standards exist for data transfer; these formats and standards are directed toward particular applications. Manchester encoding is a standard format that may be used to encode both the clock and data of a synchronous bit stream that is being transmitted over a length of interconnecting cable.
In this technique, the actual binary data to be transmitted over the cable is not sent as a sequence of logical ones and zeros. Instead, the bits are translated into a slightly different format that affords a number of advantages over using straight binary encoding. In the Manchester encoding scheme, a logical one is indicated by a zero-to-one transition that occurs at the center of bit boundaries (divisions between adjacent bits). A logical zero is indicated by a one-to-zero transition that also occurs at the center of the bit boundaries. Signal transitions may or may not occur at bit boundaries, but the information-carrying transitions always occur off-boundary. Therefore, any transition that violates these rules may be suspected as a Manchester code violation.
Manchester encoding contains not only the binary information but also a clock signal, which makes Manchester encoding a self-clocking form of encoding. A Digital Phase-Locked Loop (DPLL) may be advantageously employed to decode the binary value and timing of each bit. 10Base-T is a standard protocol that uses Manchester encoding employing a 10 megahertz (MHz) clock frequency. 100Base-TX is another standard protocol used in the transmission of binary data at a much higher frequency, thereby allowing a higher transfer rate of data. The 100Base-TX format does not use Manchester encoding.
Switching between the 10Base-T format and the 100Base-TX format currently requires that the transmitter stop transmitting the 10Base-T data to create a xe2x80x9clink downxe2x80x9d condition that the receiver can detect. After link down pause and detection, transmission of the 100Base-TX format may begin. If switching occurs before a link down pause, current receivers do not make the transition and therefore lose some or all of the data. Having to pause transmission for a link down causes transmission efficiency to suffer and the system or systems to be unavailable part of the time.
Accordingly, what is needed in the art is a more efficient way to switch transmission modes between 10Base-T and 100Base-TX modes of operation. More generally, what is needed in the art is a more efficient way for a network transceiver to switch from a first rate mode to a second rate mode.
To address the above-discussed deficiencies of the prior art, the present invention provides an auto-detection system and method for a network transceiver that allows the network transceiver to switch from a first rate mode to a second rate mode automatically. In one embodiment, the system includes: (1) an error counter, coupled to a receive input of the 10/100Base-T transceiver, that accumulates a count of Manchester code violations while the 10/100Base-T transceiver is operating in the 10Base-T mode and (2) mode-switching circuitry, coupled to the error counter, that switches the 10/100Base-T transceiver to the 100Base-TX mode when the count reaches a predetermined value.
The present invention therefore introduces the broad concept of basing mode changes from 10Base-T to 100Base-TX on error accumulations, it being assumed that error accumulations reaching a predetermined level are reasonably attributable to a change of protocol from 10Base-T to 100Base-TX. The present invention enjoys substantial utility in that manual intervention is no longer required to effect a mode change.
In one embodiment of the present invention, the error counter begins to accumulate the count upon assertion of a carrier sense signal and expiration of a predetermined wait time thereafter. Assertion of the carrier sense signal indicates the beginning of a network transmission and the onset of data that can be error-tested. The predetermined wait time (which may be factory-set or user-programmable, as desired) allows the error counter to avoid spurious noise that may be present at the inception of a network transmission.
In one embodiment of the present invention, the predetermined value is at least 16. In a more specific embodiment, the predetermined value is 32. Those skilled in the pertinent art will understand, however, that any value is within the broad scope of the present invention.
In one embodiment of the present invention, assertion of an idle signal causes the error counter to reset the count to zero. The idle signal can be asserted between the transmission of packets on the network. This puts the system in condition to begin a future accumulation and possible mode-change. One skilled in the pertinent art is familiar with packets and transmission of packets on a computer network.
In one embodiment of the present invention, the mode-switching circuitry initiates negotiation when the error counter reaches the predetermined value. For purposes of the present invention, a predetermined value is a value at which it can be determined that the received data rate is at a rate different from the current data rate and the network transceiver should negotiate to the new received data rate. Those skilled in the pertinent art is familiar with negotiation for network communications.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.